An Overview of the Use of Carbon Isotopes

The quest for knowledge and understanding of how ancient human populations evolved is based on archeological finds and artifacts that have managed to survive the passage of time and exposure to the elements. Such evidence available to scientists could provide insights into the factors that drove the evolution and development of the human race as it is now. It will also reveal how such factors led to the transformation of hunter-gatherer societies into agriculture-based societies.

The major challenge is the correct interpretation of such evidence, but even the most experienced scientists and analysts fail to completely agree on how far accepted interpretations can be considered valid and accurate.. In the absence of written or oral evidence, much of what is now known is based on what scientists have been able to infer based on the available data which are by no means infallible or completely confirmed. Because there is a dearth of verifiable benchmarks by which scientists may confidently base their conclusions, the quest is ongoing to establish them using various methods of inquiry.

One of these is the field of bioarcheology, more specifically that of reconstructing the prehistoric human diet or paleodietary studies. A study on the prehistoric human diet will provide clues as to the behavioral, societal, ecological, evolutionary and physical environment that these ancient civilizations had existed in. It may also indicate the changes in human history they had witnessed and adapted to as evidence by any shift in dietary intake that may have occurred. While much of the conclusions will be inferential, such information will nonetheless have significance in the fields of archeology, anthropology and evolutionary medicine.

Reconstructing ancient diets has gained grounds as a significant part of any archeological study, and scientists have had to rely on artifacts from archeological sites. This has led to the rise of bioarcheology as a branch of the field which specifically focus on the health, diet and daily activities of old cultures such as that of Native Americans and Southern African hunter gatherers. The literature available for the latter is especially extensive, and have had a significant impact on how anthropologist reconstruct the lifestyle of these hunter-gatherers, which in turn has shaped modern views of that type of society.

The challenge to scientists, therefore, is to substantiate these views by providing measurable evidence that can be reasonably inferred to be accurate. Furthermore, there has been a growing inquiry as to whether the descriptions of the ethnography of Later Stone Age societies as evidenced from archeological artifacts in southern Africa can be used to accurately interpret historical perspectives of the prehistoric hunter-gatherer societies .

Some of the questions that archeologists find difficult to answer are based on the variability of the societies themselves, such as the extent to which hunter-gatherers ranged over a presumably resource-rich environment, how the societal hierarchy determined the behavior of the tribe, if any existed, and whether some societies chose to stay in the coastal areas or further inland, and the reason for such decisions .

Such information is not easily acquired because the available artifacts are often insufficient to provide clear answers, and those that are analyzed are interpreted based on inferred benchmarks. One method by which scientists have endeavored to supplement geographical and archival data is to study human skeletons, basing their analysis on the chemistry and morphology of the bones and other extant biological remains such as nails and hair.

Dietary information can be determined from such analysis, and lead to suggestive information that extends beyond what had actually been eaten. Hunter-gatherer life paths, for instance, can be derived from a study of their diet because it indicates how the land was used (or not) as well as what kind of plants and animal protein they consumed which would also indicate the range of their hunting and gathering in terms of geography. It would also provide clues as to social hierarchy and organizations and the complexity associated with such dietary and subsistence behavior i.

e. the difference between the male and female diet or the importance attached to age or child bearing. This paper will provide a brief overview of the ways in which carbon isotopes have been used to reconstruct the prehistoric human diet. It will also describe current methods used in extracting the necessary components for mass spectrometer analysis and the issues that face those in the field of bioarcheology and paleodietary studies. II. Nature of carbon isotopes and its use in determining prehistoric human diets

In many instances, evidence suggests that prehistoric man were successful hunters, yet environmental remains such as fossilized plants show only that hunting and scavenging events occurred, but not what comprised the major nutritional intake of the subjects and whether such events remained a primary occupation and for how long. At issue as well is whether the effects of the shift from a hunter-gatherer society to an agricultural, domesticated society was correctly analyzed by past research in terms of societal and other behavioral aspects. To discover this, the application of stable carbon isotopes comes into play.

Carbon dating techniques have been in wide use in archeology for the last 50 years as a way to report on the evolution of the societies in terms of their lifestyles. The age of tools, clothing, jewelry and even foodstuff serve as tangible records of how people used to live during what period. The use of human and faunal bones and teeth, essentially composed of carbon and nitrogen, is an ideal source of data, providing the material needed for archeological and anthropological study where conventional sources of information are inadequate or not available.

Moreover, as humans generally derive the carbon in the body as a result from plants ingested, the idea is that it will be detected in the very bones and hair and can reasonably provide information on the type of plants eaten for up to 10 years prior to death. , The use of stable carbon isotopes as a way to reconstruct what prehistoric societies used to eat, however, is a relatively recent innovation. It was in the 1970s that the observed relationship between carbon photosynthesis and isotope ratios fueled the research that would enable the reconstruction of the prehistoric human diet.

Essentially, stable carbon isotopes could be differentiated by how they reacted to specific components of dietary plants that were incorporated into human tissue such as the heavier C3 and C4 isotopes. The reference to weight is importance. This is based on the chemical nature of isotopes that dictates how accurately one can analyze the content and profile of specific samples. Carbon isotopes, for instance, are variations of the chemical element carbon where there is identical number of protons but a different number of neutrons.

Because the atomic mass is derived from the sum of protons and neutrons, “heavier” isotopes are defined as those that have more neutrons in the nucleus than their “lighter” counterparts. Stable isotopes typically retain its properties over time as opposed to radioactive isotopes, and the archeologically important carbon isotopes are 12C and 13C. “Heavier” isotopes are typically slower to react than their “lighter” counterparts, and this difference in reaction times and movement, known as fractionation causes the isotopes to react differently to the same substances.

In terms of dietary research for prehistoric humans, laboratory standards are developed to serve as a basis for the calculation of the isotope ratio (i. e. heavier versus lighter isotope). For carbon, the laboratory standard is referred to as PDB, marine carbonate fossil (Belemnitella americana) found in the Peedee formation in South Carolina. Mass spectrometer analysis measures the amount of stable carbon isotopes in conjunction with stable nitrogen isotopes to provide the different isotope ratios present in the material being analyzed.

One good example of how the use of stable carbon isotopes has aided in understanding human prehistory is by determining at which point for specific geographical areas that the use of maize, or corn, an important C4 plant, came into prominence as a dietary resource. In general, plants are either carbon 3 (C3) that during synthesis breaks down a three-carbon molecule, or a carbon 4 (C4) plants that produce four-carbon molecules, and the difference in the rations of C4 and C3 are carbon 12 and carbon 13.

Samples of plants that are C3 are acorns, hickory nuts and wheat. In the Native American diet, for instance, studies show that the Indian’s diets underwent a significant change around the time of the Europeans’ arrival. This dietary change has been considered less than advantageous for the natives as they switched from a varied and healthy mix of seafood and various plants to a distinct, and unhealthy in the long-term, preference for the crop.

This was evidenced by the different carbon isotopic ratios of a specimen that was determined to have died prior to the introduction of agriculture and a specimen that had lived in a more agricultural society. Because the diet pre-agricultural was varied and largely unprocessed, this specimen was considered healthier than the specimen who reaped the fruits of a domesticated lifestyle, where the main emphasis was in the growing and consumption of corn and presumably domesticated i. e. “soft” animal protein.

And because an agriculture-based society will necessarily need to be more inland than a hunter-gatherer society that may well have access to the dietary resources of the sea, agriculture-based specimens would lack some of the nutrients and minerals that are derived from the consumption of seafood. Carbon isotopes also distinguishes marine and terrestrial plants and animals based on the discrepancy of ? 13C values derived from the 7%° difference in seawater bicarbonate and atmospheric carbon dioxide.